(610a) Understanding Pretreatment of Lignocellulosic Biomass With Ionic Liquid-Water Mixtures

Biomass pretreatment with certain ionic liquids (IL) can be highly effective at reducing the recalcitrance of lignocellulosic biomass to subsequent enzymatic hydrolysis; however, the IL loading must be reduced in order to improve the process economics. Pretreatment with IL-water mixture offers less IL use and is more compatible with the precedent moist biomass feeding stream and the following enzymatic catalysis and biofuel production with both favor aqueous environment. Furthermore, using IL-water mixtures could reduce viscosity and eliminate gel formation during pretreatment, facilitating scale-up and downstream processing. Previous studies have demonstrated that comparable sugar yields can be achieved at reduced IL loading (<50%) in water; however, limited knowledge is available for understanding the solvent property of IL-water mixtures and correlating cellulose digestibility with cellulose solvation and lignin depolymerization during IL-water pretreatment of lignocellulosic biomass.  In this work, we investigated pretreatment of microcrystalline cellulose (Avicel) and switchgrass with levels of 0, 20, 50, 80, 100% 1-ethyl-3-methylimidazolium acetate, [C₂mim][OAc], in water at 140-160 ^○C for 1-3h. Results indicate that the chemical composition, crystallinity and cellulose accessibility of pretreated biomass depended on IL loading and correlated with cellulose digestibility. Furthermore, Kamlet-Taft (K-T) parameters were used to predict cellulose/hemicellulose dissolution and lignin depolymerization and tied to sugar yields. In addition to the experimental study, we performed a series of molecular dynamics simulations of molecular level model of cellulose I_β dissolution in different [C₂mim][OAc]:water loading at set temperatures. Knowledge gained from this study will guide the targeted design of IL-water mixtures that are effective at solubilizing lignin/cellulose and advance the development of IL pretreatment technologies for processing lignocellulosic biomass.